In the past, there is known a reusing method for a sheet employing a decolorable colorant that is decolored if heated. In the reusing method, after a sheet on which an image is formed with the decolorable colorant is heated to decolor the image, an image is overwritten with the decolorable colorant again, whereby the sheet is reused.
In this way, in the past, the decolorable colorant is simply used as a colorant for decoloring and overwriting an image. However, it is possible that the decolorable colorant can be put to various uses. There is a demand for development of new uses of the decolorable colorant and development of an image forming apparatus that forms an image using the decolorable colorant to match the uses.